The cast hole is a hole formed in the casting by the pin attached to the mold. Because the cast hole is a hole as cast, it is inferior in dimensional accuracy. Therefore, it is preferable to add machining to the cast hole with a drill. The drill for this purpose is called a drill for a cast hole and various forms have been proposed (see, for example, Patent Document 1).
The drill disclosed in Patent Document 1 includes a land portion generally called a margin portion and a pad portion disposed rearward from the land portion in the rotational direction. Further, a pad portion is provided in the land portion. The pad portion can enhance the straightness of the drill.
However, it was found that chatter vibration occurred despite the addition of the pad portion. As a result, the position accuracy of the hole and the inner surface accuracy of the hole did not increase as expected.
Therefore, as a drill having a pad portion, a drill capable of further improving position accuracy of a hole and working accuracy on a surface of the hole is desired.